The art of chronometry has developed from a mechanical watch, comprising a spring as its power source, to a battery-powered watch comprising an electromagnetically driven tuning fork or hairspring balance and crystal to a crystal timepiece comprising a crystal oscillator which can generate a high-frequency signal as a time standard. There has also been developed a totally electronic watch which makes use of an electro-optic display element such as a liquid crystal or a light-emitting diode for displaying time and is not provided with movable parts at all.
In prior-art systems for determining the rate of a mechanical watch, the vibrations or impacts of an oscillating body incorporated in the clockwork - i.e. its ticks are detected acoustically by means of a microphone arranged outside the watch case. In a conventional system serving to determine the rate of a watch controlled by a tuning fork, having a high oscillating frequency and low ticks, or of an electromagnetically driven watch whose clockwork does not produce ticks, the generated magnetic leakage flux is electromagnetically detected by means of a monitoring coil positioned outside the watch case.
In the totally electronic watch which does not produce any tick or magnetic leakage flux, it is impossible to measure the rate acoustically or electromagnetically by the aforedescried methods. In this case, it is known to provide a lead extending through the watch case to deliver a rate signal to an external speed sensor. This conventional method, however, has the disadvantages that a circuit incorporated in the watch case is liable to be subjected to outside disturbances, that the monitoring lead occupies additional space, and that the watch must be connected through a conductor to the speed sensor every time the rate measurement is to be carried out. Thus, this prior - art method is unsuitable for testing watches on an large scale.